In communications to which real-time performance is required as in the case of feedback control, etc., communication data are required to be accumulated in some cases. For example, with respect to an in-store equipment monitoring system used in a shopping supermarket or the like, there are requirements that the temperature of equipment such as a refrigerator or the like installed in a store is kept fixed, that the monitoring state of contents in a refrigerator is left as a record, etc. In order to satisfy these requirements, a technique of accurately communication data without losing real-time performance has been known (see Patent Document 1, for example).
The patent document 1 discloses a technique of scheduling re-transmission timing at an interval period without changing a predetermined schedule in a transmitter for intermittently transmitting data on the basis of the predetermined schedule when the data do not normally arrive at a receiver.